Conventionally, a motor provided with a speed-reducing mechanism capable of large power output in spite of its small size is adopted as a driving source for a wiper apparatus incorporated in a vehicle such as an automotive vehicle, and improved in its mountability on the vehicle. For suppression of electromagnetic wave propagation to in-vehicle equipment such as a radio, a brushless motor provided with no commutator and brush may be adopted as a motor unit. As described above, by adopting the brushless motor as the motor unit, it is possible to suppress electromagnetic noises, and because of the brushless motor carrying neither commutator nor brush it is possible to realize a reduction of the motor in size and weight.
Such a brushless motor provided with a speed-reducing mechanism is descried, for example, in Japanese Laid-Open Patent Application Publication No. 2013-223317. The brushless wiper motor (simply “brushless motor”) descried in Japanese Laid-Open Patent Application Publication No. 2013-223317 includes a motor unit and a speed-reducing mechanism. The motor unit has a rotor and a rotating shaft having a worm gear integrally attached thereto. The worm gear is engaged with a worm wheel of the speed-reducing mechanism, and an output shaft is fixed to the rotation center of the worm wheel.
The rotating shaft is provided with an annular magnet for the rotating shaft which is disposed on the radial outside of the rotating shaft. The output shaft is provided with a disc-shaped magnet for the output shaft which is attached to one end in the axial direction of the output shaft. In a gear housing making up the speed-reducing mechanism, a control board (or simply “board”) is disposed so as to face the radial exterior of the rotating shaft and one end in the axial direction of the output shaft. Three Hall ICs facing the magnet for the rotating shaft and one MR sensor facing the magnet for the output shaft are provided on a surface of the control board which faces the rotating shaft and the output shaft.
According to the technique descried in Japanese Patent Application Laid-Open Publication No. 2013-223317 (FIG. 8), three Hall ICs facing the magnet for the rotating shaft are mounted on a surface of the control board which faces the rotating shaft and the output shaft, the Hall ICs being arranged at given intervals along the rotation direction of the rotating shaft. As a result, the distance between two Hall ICs disposed on respective ends in the group of three Hall ICs and the annular magnet for the rotating shaft is different from the distance between one Hall IC disposed in the middle in this group and the annular magnet. Specifically, the distance between two Hall ICs disposed on both ends and the annular magnet for the rotating shaft is relatively large, while the distance between the Hall IC in the middle and the annular magnet is relatively small. Because of this arrangement, for example, the Hall ICs on both ends may fail to detect a magnetic change caused by the rotation of the magnet for the rotating shaft, and this leads to lower detection precision.
In order to determine the distance between each Hall IC and the magnet for the rotating shaft to be the same, such an arrangement may be adopted that sensor boards carrying respective Hall ICs are prepared and set so as to face the magnet for the rotating shaft in its axial direction. In this case, however, it is necessary to prepare both the existing control board and new sensor boards. This poses a problem that the number of components increases to bring difficulty in weight/size reduction.
In addition, in order to reduce the distance between the magnet for the rotating shaft and the Hall ICs on both sides disposed along the rotation direction of the magnet for the rotating shaft, another arrangement may be adopted such that the diameter of the magnet for the rotating shaft is increased to improve its angle detection precision. In this case, however, the magnet for the rotating shaft becomes too close to the Hall IC in the middle, and this leads to problems of difficulty in laying out such components as the rotating shaft, magnet for the rotating shaft, and Hall ICs, and of an increase in size of the motor for ensuring a clearance between the magnet for the rotating shaft and the Hall ICs.